1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a semiconductor device having a capacitive element utilizing an interconnection layer.
2. Description of the Background Art
Recently, capacitive elements utilizing a parasitic capacitance between interconnections have started to be used along with process miniaturization. A semiconductor integrated circuit device having such a capacitive element is disclosed for example in Japanese Patent Laying-Open No. 2001-177056. The semiconductor integrated circuit device disclosed in Japanese Patent Laying-Open No. 2001-177056 includes a first electrode, a second electrode, and a dielectric film sandwiched between the first and the second electrodes, constituting a capacitive element. The first electrodes and the second electrodes are arranged to face each other in a plane direction and a thickness direction of a semiconductor substrate.
Japanese Patent Laying-Open No. 2002-100732 discloses a method of forming a capacitive element in which at least two interconnections formed in an identical interconnection layer are arranged in proximity to each other to obtain an interconnection capacitance serving as a capacitive element.
Further, Japanese Patent Laying-Open No. 2003-152085 discloses a semiconductor device for preventing noise coupling to an MIM (Metal-Insulator-Metal) capacitance and a method of manufacturing the same. The semiconductor device disclosed in Japanese Patent Laying-Open No. 2003-152085 includes a semiconductor substrate, a capacitive element formed above the semiconductor substrate, and at least a shield layer formed above or below the capacitive element. In another semiconductor device, a stacked film electrically connected to the shield layer is formed in the same layer as the capacitive element to cause the stacked film to operate similarly to the shield layer.
Furthermore, a capacitive element utilizing an interlayer capacitance between interconnection layers is disclosed in “Capacity Limits and Matching Properties of Integrated Capacitors” by Robert Aparicio et al., IEEE Journal of Solid-state Circuits, Vol. 37, No. 3, March 2002, pp. 384-393.
However, the semiconductor integrated circuit device disclosed in Japanese Patent Laying-Open No. 2001-177056 and the method of forming a capacitive element disclosed in Japanese Patent Laying-Open No. 2002-100732 do not include a measure to reduce interference with the capacitive element by an external circuit. Consequently, there arises a problem that the capacitance of the capacitive element fluctuates. Particularly, as an external circuit such as a digital portion progresses to operate faster, the measure against such a problem is increasingly required.
Further, in the semiconductor integrated circuit device or the like disclosed in Japanese Patent Laying-Open Nos. 2001-177056, 2002-100732 and 2003-152085, if interconnection layers and silicon gate layers are arranged with uneven density, the unevenness will cause a difference in the progress of etching. Thus, the configuration obtained at the end of the process may have a non-uniform finish. Furthermore, if an active region and the like formed in a main surface of the semiconductor substrate does not have an area satisfying a predetermined ratio to a fixed region on the main surface, it is not possible to form a layer uniformly over the main surface. Thus, it becomes difficult to control etching appropriately when forming a capacitive element on the film. For these reasons, it is not possible to form a capacitive element offering a desired characteristic.